Many power and automation technology applications require resistive materials whose resistance or specific resistivity can be adjusted. Depending on the application, a resistive material should carry e.g. nominal and fault currents up to at least a few tens of kA and more, and support voltages of more than 1 kV. Resistances ranging between a 1 mΩ and a few Ω, say 5Ω, may be required.
Graphite materials have a specific resistivity that can be adjusted by adding suitable materials. However, Graphite can overheat locally when inhomogeneous currents are applied, since its capacity for distributing the current homogeneously is poor. Thus, hot-spots are formed and the material deteriorates or may even disintegrate.
FR 940 438 discloses a layered electrical resistance with great power dissipation. The resistor is built from resistive elements that have metal-coated faces for contacting each other. In addition, wing-like cooling elements made from metal can be interposed in an alternating sequence with the resistive layers. A low contact resistance is achieved by arranging discs made of soft metal between the resistive elements and/or the cooling elements. Very high overall resistance values are achieved owing to the bulk resistance of the resistive elements.
U.S. Pat. No. 1,956,859 discloses a stacked electrical resistor with resistor blocks spaced apart by washers and connector strips and with the blocks being clamped or bolted together. Again, large resistances are obtained owing to the bulk resistances of the resistor blocks.
U.S. Pat. No. 3,227,983 relates to a stacked electrical resistor of similar type with certain improvements, such as resistor elements having different thickness, being made of carbon powder, being coated e.g with powdered copper, being held together by clamping means, or being bonded together via their confronting high conductivity coatings. The overall resistance is again determined by the sum of the bulk resistances of the resistor elements.